1. Field of the Invention
This invention relates to a device and method for the treatment of specific areas of inner surfaces of biological conduits with medicaments.
2. Previous Art
Atherosclerosis is a progressive disease wherein fatty, fibrous, calcific, or thrombotic deposits produce atheromatous plaques within and beneath the intima which is the innermost layer of arteries. The most commonly affected vessels are the aorta, iliac, femoral, coronary and cerebral arteries. Untreated coronary artery disease can lead to angina, hypertension, myocardial infection, strokes and the like. Atherosclerotic blockages can occur anywhere within the thicket of vessels and arteries that service the heart. Regions of blood vessels that are blocked by atheroma (plaque) or other materials are generally referred to herein as stenotic regions, and the blocking material as stenotic material. The composition of the stenotic material can vary from hard calcium-containing lesions to fatty lipid-based coatings on the inside of the coronary arteries. Stenotic materials deposited on blood vessel walls are often relatively soft and tractable. However, in many cases, the stenotic material may contain a significant amount of calcified and hardened material. A number of methods such as coronary artery bypass graft (CABG) surgery, percutaneous transluminal coronary angioplasty, (PCTA), direction coronary atherectomy (DCA), energetic ablation, and stenting, are used in attempts to restore the narrowed blood vessels to, as close as is possible, to their original diameters. In percutaneous transluminal coronary angioplasty, sometimes called balloon angioplasty, during coronary catheterization, an inflatable balloon is inserted in a coronary artery in the region of coronary stenosis. Inflation of the balloon for 15-30 seconds results in an expansion of the narrowed lumen or passageway. Devices suitable for PCTA have been described is U.S. patents such as U.S. Pat. No. 4,323,071. Directional Coronary Atherectomy is a procedure which has been developed for excising and removing stenotic material from the vascular system. DCA procedures employ a variety of special catheters having tissue cutting members (cutters) located at the distal end of the catheter. In use, the catheter is inserted into a biological conduit so that the cutter housing is placed adjacent to the stenotic region with the housing window aligned to the stenotic material. Stenotic material is invaginated into an opening in the cutter housing by inflating a balloon opposed to the housing window. Simultaneous rotation and translation of the cutter sever the stenotic material which is retained in the nosecone at the distal end of the catheter. Examples of such devices can be found in U.S. Pat. Nos. 5,312,425; 5,250,959; 5,181,920; 5,071,425; 4,979,951; 4,781,186; and 4,669,469 (reissued as No. Re. 33,569), herein incorporated by reference in their entirety. Ablative methods such as the application of laser energy to the atheroma or high speed abrasive burrs are also used to widen the blood vessel at the point of stenosis. Another method of treatment of cardiac insufficiency employs stents, (mechanical supports). Stents are placed at the site of the stenosis and expanded to widen the blood vessel. The stent remains in place as an arterial implant. All of these techniques are used to open blocked areas of blood vessels in an attempt to restore the original lumen diameter or provide an alterative path for blood flow. Although these methods of treatment are distinct different methods, they share one common problem, restenosis. A certain percentage of the treated blood vessels will reocclude (restenose) after a period of time. Restenosis can occur in as many as 30-40% of the cases. In such restenotic instances, the original procedure may be repeated or an alternative method for achieving blood flow may be tried. The common factor in all of these treatment methods is that they all traumatize the blood vessel to some extent. There are several reasons why restenosis can occur. One is that small clots form on the arterial wall. Tears in the wall expose blood to foreign material and proteins, such as collagen, which are highly thrombogenic. Resulting clots can grow gradually, or can contain growth hormones which are released by platelet within the clot. Additionally, growth hormones released by other cells, such as macrophages, can cause smooth muscle cells and fibroblasts in the region to multiply. Further, there is often complete loss of the normal single layer of cells constituting the endothelial lining following angioplasty. This layer normally covers the internal surface of all vessels, rendering that surface compatible, i.e., non-thrombogenic and non-reactive with blood. Mechanically, when as angioplasty balloon is inflated, the endothelial cells are torn away. Prior art procedures also produce injuries in the arterial wall which become associated with inflammation. Any kind of inflammatory response may cause the growth of new tissue. In order to address such problems, the cardiology community needs to administer drugs which are biocompatible and in such concentration that they do not induce a toxic reaction.
Some drugs might have a beneficial effect upon inhibition of the stenotic growth or even remove the stenotic material but, treatment of the site of vessel blockage via systemic administration of drugs has not been successful. The area in need of treatment is very small relative to the area of the vascular system. Blood flow at the stenotic region is low and variable. Localized application of some drugs could achieve the most effective result without burdening the entire system with large amounts of a drug. One attempt to localize drug delivery during an angioplasty procedure is described in U.S. Pat. No. 5,199,951. This patent is limited in the area of treatment, and method of application. There does not exist an efficient means for the localized delivery of medicaments in a biological conduit such as a blood vessel.
What is needed is a method of applying a medicant to a specific site in a biological conduit to either remove or destroy the stenotic material or to treat the site of vascular intervention to prevent restenosis.